Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Evaporator Temperature Sensor: Operation
The Body Control Module (BCM) will send a Programmable Communications Interface (PCI) bus message to the Powertrain Control Module (PCM), which will check engine, coolant temperature, and refrigerant pressure temperature before turning ON the A/C Compressor Clutch. Turning ON the A/C Compressor Clutch will allow the system to cool the evaporator. The BCM will send a message to the PCM when the evaporator temperature becomes too cold. The PCM will then turn OFF the A/C Compressor Clutch, before evaporator freeze up occurs. The DRBIII(R) scan tool can be used to monitor this operation. The temperature set point at which the clutch is turned OFF varies with the outside ambient temperature. The temperature at which the clutch is turned ON is preset to 2- F above the OFF setpoint mentioned above. Refer to EVAPORATOR TEMPERATURE SENSOR SET POINT table and (Fig 1 ) for the correct setpoint.
| AMBIENT TEMPERATURE SENSOR READING °F (° C) | A/C CLUTCH OFF EVAPORATOR TEMPERATURE SET POINT ° F (° C) |
|---|---|
| 185 (85) | 31 (-0.5) |
| 100(37.7) | 31 (-0.5) |
| 77 (25) | 34(1.1) |
| 60(15.5) | 35(1.6) |
| -70 (-56.6) | 36 (2.2) |
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.